The present invention relates to an apparatus and method for making an electrical heating device. More particularly, the present invention relates to the use of conductive and non-conductive inks to form a heating device on a substrate which is then encapsulated in an insulating material to provide a body portion of the heating device.
An object of the present invention is to provide a heating apparatus which is inexpensive to manufacture, reliable, and which can be used for a variety of heating applications. For instance, the heating device for the present invention may be used as a liquid heater for heating water, coffee, tea, coolants, glues, oils, or other suitable liquids. In addition, the heating device of the present invention can be used as a dispenser to change a solid or liquid into a gaseous state. This can be used to dispense fragrances, insect repellents, vapors for health care purposes, or other suitable substances. The present invention may further by used for thermostat heaters, heaters for automotive applications such as battery warmers or mirror heaters, or for heating various other types of substrate materials.
A first aspect of the invention is the provision of a substrate material to which a polymer thick film (PTF) carbon ink is applied. The substrate material must meet certain temperature requirements so that it will not melt or deform at the designed heater temperature requirements. Examples of substrate materials which may be used include ceramic, glass, silicone, or printed circuit board material. The substrate size will depend on the heat requirements.
A second aspect of the invention is the application of PTF carbon ink to the substrate to form a resistive heater. The carbon ink is applied to a first portion substrate using a screen press or by a spraying method. The geometric shape of the PTF ink heater is a matter of design and will be determined by application specific requirements.
A third aspect of the invention is the application of conductive leads to the substrate. In order to produce a PTF carbon ink heater which produces the required amount of heat, low resistance leads are needed to carry electrical current to the PTF carbon ink. These leads may be produced using a PTF base material impregnated with silver or copper particles. The PTF conductive lead material may be applied to the substrate before the PTF carbon ink is applied, or it may be applied over the PTF carbon ink, as long as the conductive leads and the carbon ink overlap. The PTF conductive lead material may be applied to the substrate by printing or spraying methods.
A fourth aspect of the invention is coupling first and second electrodes to the conductive leads. The electrodes provide power to the conductive leads and to the carbon ink to cause heating of the device.
A fifth (and optional) aspect of the invention is the application of a resistive film to a second portion of the substrate and the application of a conductive film to the substrate to form third and fourth conductive leads engaging the resistive film on the second portion of the substrate. An electrical component may be coupled to the third and fourth conductive leads prior to encapsulating the heater apparatus.
A sixth aspect of the invention is overmolding a plastic body around the heater. The method used to form the plastic body is preferably an injection molding process which molds an insulating plastic material around the substrate and PTF carbon and conductive heater. Examples of plastic materials which may be used include but are not limited to polypropylene, polyphenylene sulfide, polyetherimide, polycarbonates, or polyvinyl chloride.
According to the present invention, a heater apparatus includes a substrate, a resistive film formed on a first portion of the substrate, and first and second conductive leads formed on the substrate engaging the resistive film. First and second electrodes are coupled to the first and second conductive leads, respectively. The heater apparatus also includes an overmolded body made of an insulating material formed on the substrate to encapsulate the resistive film, the first and second conductive leads, and a portion of the first and second electrodes in an insulating material.
The substrate is formed to include first and second apertures in close proximity to the first and second conductive leads, respectively. The first and second electrodes each include a tab portion extending through the first and second apertures, respectively. The tab portions are deformed so that the tab portion of the first electrode engages the first conductive lead and the tab portion of the second electrode engages the second conductive lead.
The apparatus may further include a resistive film formed on a second portion of the substrate, and third and fourth conductive leads formed on the substrate engaging the resistive film on the second portion of the substrate. An electrical component is electrically coupled to the third and fourth conductive leads. The overmolded body is configured to surround at least a portion of the electrical component in insulating material to couple the electrical component to the heating apparatus.
According to a second embodiment of the present invention, an electrical component is provided which includes first and second conductive leads extending from the electrical component. The electrical component is configured to be slidably inserted between said first and second electrodes of the heating apparatus so that the first conductive lead engages the first electrode and the second conductive lead engages the second electrode, respectively, to couple the electrical component to the heating apparatus. The electrical component includes an insulated housing and the first and second conductive leads extend outwardly from the insulated housing. The insulated housing includes first and second contact support posts abutting the first and second conductive leads. The first and second contact support posts hold the first and second conductive leads against the first and second electrodes, respectively, upon insertion of the electrical component between said first and second electrodes. The insulated housing further includes a partition formed between the first and second contact support posts for separating the first conductive lead from the second conductive lead. The insulated housing still further includes a front portion and a rear portion coupled to the front portion to define an interior region therebetween and a current carrying device positioned within the interior region. A voltage dropping resistor is coupled to the first conductive lead to supply current to the current carrying device.
Also according to the present invention, a method is provided for making a heating apparatus. The method includes the steps of providing a generally rigid substrate, applying a resistive film to a first portion of the substrate, and applying a conductive film to the substrate to form first and second conductive leads engaging the resistive film on the first portion of the substrate. The method also includes the steps of coupling first and second electrodes to the first and second conductive leads, respectively, and molding an insulating material to the substrate to form a generally rigid insulating body encapsulating the resistive and conductive films.
The coupling step of the method includes forming first and second apertures in the substrate in close proximity to the first and second conductive leads, respectively, and inserting a portion of the first and second electrodes through the first and second apertures, respectively. The coupling step also includes deforming the portion of the first and second electrodes extending through the first and second apertures to engage the first and second conductive leads, respectively, thereby electrically coupling the first and second electrodes to the first and second conductive leads.
The method may further include the steps of applying a resistive film to a second portion of the substrate and applying conductive film to the substrate to form third and fourth conductive leads engaging the resistive film on the second portion of the substrate. This provides a supplemental contact for electrically coupling an electrical component to the heater apparatus. The method still further includes the step of coupling an electrical component to the third and fourth conductive leads prior to the molding step. The molding step also encapsulates at least a portion of the electrical component in insulating material to mechanically couple the electrical component to the heating apparatus.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of a preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.